This invention relates to fuel cell structures and more particularly to improved electrical bus connection structures for bringing electrical power out of a high temperature fuel cell generator. The invention is more particularly directed to high temperature solid electrolyte fuel cells which utilize an electrochemical combustion reaction between an oxidant and a fuel gas, which are combined at the fuel electrode to directly convert chemical energy of the fuel into direct current electrical energy. A typical such fuel cell reacts hydrogen with oxygen or air to produce electrical energy, water vapor and heat.
Solid oxide electrolyte fuel cells operate at elevated temperatures of from about 700.degree. C. to about 1100.degree. C. in order to render the solid oxide electrolyte sufficiently conductive to achieve high conversion efficiency. At such high temperature the need for expensive electrode catalysts is eliminated and gaseous fuels such as hydrogen and carbon monoxide are combusted spontaneously at the fuel electrode.
A solid oxide electrolyte fuel cell is described in co-pending application Ser. No. 219,204, filed Aug. 28, 1981, entitled "High Temperature Solid Electrolyte Fuel Cell Configurations and Interconnections", which can be referred to for further details regarding the fuel cell. This co-pending application describes a fuel cell structure with elongated annular cells connected at adjacent cells along the full axial length of the cells. A fuel cell electrical generator utilizing such elongated annular fuel cells is described in co-pending application Ser. No. 219,185, filed Aug. 19, 1981, entitled "Fuel Cell Generator", and providing further details for a generator formed using solid oxide electrolyte fuel cells.
In the fuel cell and fuel cell generator structures set forth in the above-mentioned co-pending applications, the electrical connection or contacting of output buses to the high temperature fuel cell electrodes is carried out in a high temperature zone within the generator with the output buses then being brought through the generator housing for interfacing with an electrical load line at near ambient temperature. The output electrical buses must be large area, high-conductivity conductors, which means that they are also excellent thermal heat sinks which conduct heat away from the fuel cell members with which they are in physical contact. The thermal conduction away from the fuel cell structures through the bus conductors can result in non-uniform fuel cell cooling at the points of contact between the bus bars and the fuel cell structures. In addition, cold spots can occur in regions near the bus bars where radiation cooling would lead to unacceptable temperature gradients in the fuel cell array of the generator. These temperature gradients can cause physical distortion and, in the worst case, cracking of the elongated tubular fuel cell elements which would permit mixing of the fuel gas and oxidant at an area other than the solid electrolyte. The fuel and oxidant must be maintained separated across the electrolyte barrier to avoid wasteful combustion. This means fuel or oxidant is introduced within the tubular cell with the other reactant supplied about the exterior of the tube. Non-uniform temperature distribution within the fuel cell assembly threatens the mechanical integrity of the fuel cell assembly as well as interfering with good electrical contact along the length of the fuel cell assemblies.
In general, high temperature electrochemical devices require efficient electrical connection means which do present inherent heat loss paths from the devices, but in such electrochemical device's failure to reduce the heat loss or control the uniformity of heat flux distribution does not threaten operability of the device. In the high temperature, solid oxide electrolyte fuel cells with which the electrical contact structure of the present invention find application, continued reliable operation of the cells is dependent on limiting heat flux losses and providing a highly uniform heat flux distribution.
A solid electrolyte fuel cell is described in U.S. Pat. No. 3,668,010 in which annular electrodes are disposed on a solid tube support, with electrode ends overlapping and electrically connected by conductive material. The cells are interconnected in rows by metal strips with the rows being segregated by heat insulating material.
The present invention is directed to providing good electrical conductivity bus bar interconnection to a fuel cell array with minimal thermal losses and avoidance of localized cooling. An improved electrical bus connection means is provided for improved structural stability for the fuel cell tubular array and for the interconnection between the fuel cell and the output buses.